Corona treatment is a method using an electrical corona discharge to modify a surface of a web to improve its ability to accept inks and adhesives. In a corona treatment system, a high voltage electrode is mounted parallel to and spaced from a ground roller, which forms a grounded electrode. The air gap between the electrode and the ground roller is energized, forming a corona, which, when web is passed therethrough modifies the material the web is formed of, and makes the web more receptive to ink and adhesives. Corona will be produced anywhere there is air within this air gap.
The web is moving a high speed. As the web enters into the corona treatment system, the web passes through a pair of nip rollers, and may pass through a secondary pair of nip rollers. The web is routed around idler rollers and then through the air gap between the electrode and the ground roller. After the web is treated, the web exits the corona treatment system.
It is desired for the air within the corona treatment system to be kept inert to provide for a better reaction within the air gap. When a web is moving at high speed, the web entrains air in the ambient atmosphere and enters into the corona treatment system through the nip rollers. The air has a tendency to permeate the corona treatment system which may result in an undesirable reaction in the corona treatment system.